The invention relates to the production of sanitary articles intended to absorb and retain body fluids.
When the absorbing article in place is impregnated with such body fluids, in particular urine, powerful and unpleasant smells are produced. The predominant smells among these are ammoniacal smells due to the ammonia originating from the hydrolysis of urea by the ureases of bacteria (Proteus, Acinetobacter, and the like) present on the skin and in the digestive tract.
For the purpose of suppressing these smells, widespread recourse has been had to absorbents of smells or ammonia (U.S. Pat. No. 3,340,875, Scott Paper Company), optionally in combination with deodorants, fragrances, and the like. The use of pH buffers (WO-A-94 25077), of oxidants (hydrogen peroxide, chlorine dioxide), of biocides (metals or of metal cations), as well as of bactericides (quaternary ammoniums, in particular), of antibiotics, of complexing agents or of surfactants, both alone and in combination with one another, has also been recommended. These various products present the general problem of an irritant effect on the skin and mucosal mebranes. Absorbents of smells or of ammonia are certainly less dangerous in this respect but they leave the field free for a bacterial growth which remains worrying and which it would be advisable to control from the outset. The way which appeared necessary for the control of the bacterial emission of ammonia from urea consists in inhibiting the enzymes which are responsible for it, that is to say the ureases.
The use of urease inhibitors of low or moderate activity has until now only been envisaged in combination with ammonia scavengers (JP 61-179155). Some powerful urease inhibitors, such as hydroxamic acid derivatives (U.S. Pat. No. 3,920,015, Allied Chem. Corp.), are advantageous but their toxicity excludes them from the targeted use. Others, such as phenyl phosphorodiamidate (PPDA) or dimethyldithiocarbamate (DTC), are compounds which are very effective against the formation of ammonia but give rise, during their use, to other very unpleasant sulfurous or alliaceous smells which are perhaps related, at least in part, to their own decomposition by the bacterial flora present.
The search for a solution to this problem is all the more pressing since, nowadays, the absorption capacity for body fluids of protection articles has been very substantially increased by incorporating superabsorbent polymers (SAP) into them, in particular hydrophilic polymers and copolymers of acrylic acid, and since, by the same token, the time during which they are maintained in place has been increased, all conditions which promote the development of microbial and enzymatic activity and of the smells which result therefrom.
It has now just been found that it is possible to formulate superabsorbent polymers with certain boron derivatives in order to prepare therefrom compositions which, although impregnated with urine or with biological fluids containing it and maintained under conditions of use which are especially propitious for bacterial growth, give rise neither to significant evolution of ammonia nor to repellent or simply unpleasant smells and which communicate this property to the sanitary articles which contain. them.
The invention thus consists of a superabsorbent composition intended for production of sanitary articles of the underwear, diaper or disposable diaper type which do not develop unpleasant smells which comprises a polymer, which is superabsorbent with respect to water, saline solutions and body fluids, and sodium tetraborate or sodium metaborate in the proportion of 0.1 to 10% of boron derivative, preferably 0.5 to 5%, with respect to the superabsorbent composition.
Superabsorbent polymers within the meaning of the present invention are polymers which result from the polymerization, with partial crosslinking, of watersoluble ethylenically unsaturated monomers, in particular acrylic and methacyrlic acids and their alkaline salts, whether they are obtained by an inverse suspension or solution polymerization process. These polymers possess a very high capacity for absorption and retention of water and aqueous solutions and are nowadays widely available commercially in the form of powders with particle sizes of between 100 and 800 xcexcm. The literature relating to them is very extensive; reference may be made, for example, to EP-A-0,312,952 (The Dow Chem. Co.) and to EP-A-0,441,507 (Sumitomo Seika Chem.).
Within the meaning of the present invention, sodium tetraborate (Na2B4O7) is the anhydrous, pentahydrate or decahydrate (borax) salt and the metaborate (NaBO2) is also regarded independently of its degree of hydration. These boron compounds are mixed with the polymer in the powder form in proportions indicated above.
The preparation of the composition according to the invention is very easy, since it is sufficient to incorporate the boron derivative in the powder form, preferably with a particle size also of between 100 and 800 xcexcm, in the superabsorbent polymer powder by simple mixing. However, it has been observed that, if the boron derivative was introduced within the superabsorbent polymer particles, an odor-preventing efficiency was obtained, at equivalent concentration, which is greater than by simple mixing of the powders. This results in an alternative form of the process, which also forms part of the invention, whereby the polymer powder is swollen using an aqueous solution of boron derivative and then the water thus introduced is evaporated.
The superabsorbent compositions of the invention become gelled on contact with water, aqueous saline solutions or body fluids, like the superabsorbents of the prior art, and the gels thus formed behave in a substantially identical way. They do not suffer from any counterindication, the boron derivatives which are the means of the invention being rightly regarded as inoffensive and being widely used in various mild antiseptic compositions at contents of the order of 1% by weight. They are used in place of the ordinary superabsorbents in the manufacture of sanitary articles such as disposable diapers for babies, for young children, for adults or for elderly people of both sexes. This use also constitutes a subject of the present invention.
Assessment of -the true effectiveness of odor-preventing products is difficult to carry out. Since the invention comes within the context of urease inhibitors, the candidate compounds which can be envisaged for their anti-urease activity are therefore generally classified by an IC50 value according to the results of an enzymatic test which will be described later. Since the process which generates smells is a biological process, it is necessary to be able to estimate the effectiveness of various urease inhibitors for their ability to limit the biological emission, by urea-fermenting microorganisms, of at least the most common odorous compound, in this case ammonia. This effectiveness is understood of the inhibitor just as it is or In the presence of various substances with which it is combined in the production of diapers and other sanitary articles, in particular superabsorbent polymers. The results of this test correlate fairly well with the IC50 values. Finally and particularly, it is necessary to be able to decide on the satisfactory overall result by olfactive tests under conditions which give acceptable simulation of the conditions of use of the products in which the superabsorbent composition which is believed to inhibit smells is incorporated. They are carried out by impregnating a disposable diaper with urine under standardized conditions, by heating the combination in an oven at a low temperature and by subjecting the object to a nose panel for overall assessment of its possible unpleasant smells.
Such tests are described in the examples given below, which illustrate the unexpected effectiveness of the products according to the invention. In these tests, the superabsorbent polymer used is a partially neutralized polyacrylic acid marketed under the name of AquaKeep(copyright)D (Elf Atochem S.A.).